Array-based light-emitting systems present unique testing challenges. One challenge is to determine the electrical and optical characteristics of both the full array and the individual light emitters. Determining the array characteristics becomes more difficult as the physical size of the array increases. One standard characterization technique for light emitters is the use of an integrating sphere, in which all of the light emitters are simultaneously energized and the optical characteristics of the array as a whole are determined. Thus, for array-level measurements, integrating spheres may be used, but with a number of limitations.
Large integrating spheres that are, for example, 1 or 2 meters in diameter, are available, but these are expensive and may still be insufficient for very large arrays having one or two lateral dimensions on the order of meters. Arrays on flexible substrates may be curled or folded to fit into a sphere, but this requires manual handling, decreases throughput, and possibly introduces inaccuracy or reproducibility issues in the measurements. In particular, variations in the physical configuration of the array will require the generation of new calibration files, again reducing throughput and increasing testing costs. Arrays on rigid substrates simply may be too large to fit within an available sphere. Another concern is that integrating sphere measurements typically require a relatively long duration, in part because of the need to provide sufficient time for the system to reach thermal equilibrium. Such equilibration times may be on the order of tens of minutes, resulting in relatively low throughput of the test system.
In order to characterize each light emitter individually, the light from each light emitter must be analyzed separately, which cannot be done in a full sphere measurement of the array. One approach to addressing this problem is to individually energize each LED for its own measurement. However, this may require special or additional wiring on the array circuit board that is only used for testing purposes, adding further cost to the lighting system. Another approach is to energize the array and measure each light emitter separately with a small integrating sphere that covers only one light emitter at a time. Obviously such approaches can take a great deal of time for a large array, and may also not be able to achieve the required level of accuracy because of the relative size of the sphere to the light emitter.
In view of the foregoing, a need exists for systems and techniques enabling the characterization of array-based lighting systems capable of providing high accuracy and throughput at low cost.